Deriving class from `object` in python

问题:

So I'm just learning python (I know plenty of other languages) and I'm confused about something. I think this is due to lack of documentation (at least that I could find). On a few websites, I've read that you should derive your classes from object:

class Base(object):
    pass

But I don't see what that does or why or when you should do it. Is there official documentation on this that I've missed? Is this a 3.x feature?

回答1:

Mostly it isn't going to matter whether or not you inherit from object, but if you don't there are bugs waiting to catch you out when you've forgotten that you decided not to bother.

Some subtle things just won't work properly if you don't ultimately inherit from object:

1. Using properties in classic classes only partly works: get works alright, but set does weird things.
2. Multiple inheritance behaves differently in classic classes than in classes derived from object.
3. Also multiple inheritance won't work if you try to mix classic classes with those that subclass object. Whatever you do you want to be consistent.

Some people are fine with continuing to use classic classes except when they need the new behaviour, others say to always use new style classes to avoid later shooting yourself in the foot. If you're working on a single person project do whatever is good for you; if its a shared project be consistent with the other developers.

回答2:

Start here: http://www.python.org/doc/newstyle/

Also, read this: http://docs.python.org/release/2.5.2/ref/node33.html

It is one of several Python 2 interim solutions that will no longer be needed in version 3.

回答3:

In Python 3, classes extend object implicitly, whether you say so yourself or not.

See here.